Magnetostrictive device and alloy and method of producing them



Aug. 15, 1950 2,519,277

E. A. NESIBITT ET AL MAGNETOSTRICTIVE DEVICE AND ALLOY AND METHOD OF PRODUCING THEM Filed Jan. 15, 194"! MMHETUSTRICTIVE CORE FORMED 0F IRON-COBALT- VANADIUM ALLOY HEAT mam) BETW sew sao c. .uva coo-c.

FIG. 2

= V Pus'nc HOUSING 6 EFFICIENCY 01v Q REMANENCE E $2 1 so came/vi 3 i FORCE 3 40 g E g a 5. E A NESB/TT INVENTORS: J WILLIAMS 00 ANNEALING TEMPERATURE C.

Patented Aug. 15, 1950 2,519,277 MAGNETOSTRICTIVE DEVICE AND ALLOY AND METHOD Ethan A. Nesbitt and ham, N. J assignors tories, Incorporated, New

ration of New York F PRODUCING THEM Howell J. Williams, Chatto Bell Telephone Labora- York, N. Y., a corpo- Application January 15, 1947, Serial No. 722,242 Claims. (Cl. 175-21) This invention relates to magnetostrictive devices and to materials suitable for use in such devices and to methods of producing such devices and such materials.

In particular, this invention relates to magnetostrictive devices in which the magnetostrictive element is made of a permanently magnetized body of an alloy comprising cobalt and iron, preferably with a small amount of vanadium added, which has been subjected to a special treatment comprising working and heating. Such a treatment gives a suflicient coercive force to the alloy so that a magnetostrictive element made from it may be efficiently operated entirely on remanence without the aid of an external polarizing device.

In using magnetostrictive devices having magnetostrictive elements which vibrate mechanically under the influence of a magnetic winding supplied with an alternating current, it has been found that the greatest degree of magnetostriction' is obtained when the vibrating element is magnetically polarized. This polarization is also necessary in order to bring the total flux density within the element to a point at which there will be no reversal of magnetic flux direction in the magnetostrictive device throughout the alternating current cycle, and at which the change in dimensions of the element will be substantially proportional to the change in flux density so that the wave form of the mechanical vibrations of f the magnetostriction element will conform as nearly as possible to the wave form of the alternating current applied to it.

Ordinarily, the polarization of the magnetostriction element has been accomplished by means of an external direct current winding applied to the element, by means of a direct current superimposed upon the alternating current winding or, by a permanent magnet placed in the magnetic circuit of the element. The use of the external winding or superimposed direct current or the permanent magnet to polarize the element presented difiiculties since the external winding andthe superimposed direct current required a source of power, while if the external permanent magnet was used the device did not operate in a closed magnetic circuit. Also, the use of an external polarizing winding or Of an enlarged alternating current winding to carry the extra biasing current together with the required additional power supply, or the use of an external permanent magnet, took up extra space which was undesirable in equipment where available space was at a minimum.

In the device of the present-invention the above-described difliculties are avoided by using, for the magnetostrictive element, an alloy of cobalt and iron (preferably containing a small amount of vanadium) which has been subjected to a special treatment which confers on it a sufficiently high coercive force so that the vibrating element may be operated entirely on remanence for most purposes without being demagnetized by the alternating current required. This does away with the necessity of using the external polarizing winding or magnet with the resulting saving in space and power. Even for uses requiring large values of alternating currents which would, in the absence of a biasing field, tend to demagnetize the magnetostrictive cores of the present invention, such cores are desirable since they reduce considerably the necessary size of supplementary biasing equipment.

It has been known that alloys of cobalt and iron or of vanadium, cobalt and iron are useful as magnetic materials. However, it was not previously known that such alloys, having a certain range of composition if given a special heat treatment, would acquire properties rendering them suitable for use as vibratory magnetostrictive elements without a biasing field. The present invention provides a method of treating such alloys to make them suitable for such use in magnetostrictive devices.

According to the present invention, in its preferred form, vibrating magnetostrictive elements are made from an alloy comprising 2 per cent by weight of vanadium, 49 per cent by weight of cobalt and 49 per cent by weight of iron, which has been cold worked and then annealed at from 450 C. to 650 0. Although this range is the preferred composition, favorable results are also obtained when the alloy comprises from about per cent to about eper cent by weight of vanadium, about per cent to about '70 per cent by weight of cobalt and the remainder iron. Good results are also obtained with alloys having similar proportions of cobalt and iron and containing less vanadium or none at all.

Good results are obtained when these alloys are formed of the purest ingredients with the least inclusion of impurities or modifying ingredients. However, when the alloy is formed of commercial substances, there will ordinarily be small amounts of impurities present but such impurities should ordinarily be kept below about 1 per cent total and preferably below about per cent. Particularly harmful impurities such as carbon and sulphur should be avoided in so far as possible. Carbon is preferably not present in 3 4 amounts greater than about .1 per cent. Desul- Fig. 2 i a perspective vi w r a fini hed unit phurization by addition of manganese to the melt employing a vibrating element as shown in Fig. 1, ordinarily results in an adequate removal of sulportion of the unit being broken away to show phur. The manganese remaining in the alloy the construction thereof; and

silicon may often be present in amounts up to Fig. 1 when the magnetizing winding is energized per cent each. with alternating current without a direct current The first step in the treatment of these alloys bias.

to produce the desired magnetic pr per i s p n The beneficial which the present invention is depend nt is a described treatment of the alloy comprising vacold working of the alloy. This cold working is nadium, cobalt and iron are shown clearly in the though obviously other common forms of cold coercive force with the annealing temperature deformation of the metal may be employed. This and also the variation of the efficiency of the cold working step is essential to the development material operating on remanence with the anof the desired coercive force in the alloy. healing temperature. These results were obdeveloped when the alloy is cold rolled to a thickequal parts by weight of iron and cobalt and 2 alloy is to be rolled into thin tapes, as is prefrolled into a tape 2 mils in thickness and formed erable for the formation of'the magnetostrictive into a magnetostrictive device as shown in Fig. 2 devices of the present invention as will be deand described more fully below Analogous rescribed in more detail below, thickness reducsuits are obtained with devices formed from altions of the order of 90% or more may be found loys having different proportions and from alloys desirable. There is no limit to the degree to containingno vanadium.

which the thickness may be reduced except for As may b able devices to produce a uniform tape at excesmaterial is annealed at about 550 C., while the insome instances even less. 650 0. although ordinarily it is more desirable The second step in the treatment of the alloy to remain within the range of 500 to 600 C.

is a heat treatment. e preferred temperature aterials treated in accordance with the presnge for heat treating the material is from about ent invention may be employed in the form of a C about 600 e temperature of spirally wound tape core In such as that shown in heating depends partly on the use to which the Fig. 1. In forming such a core 10, the material about 525 C. and 600 C. as the matter of fabricating, handling and windis not criti the conditions heretofore described.

The alloy which has been treated according After annealing, the core I0 is removed from process will when magnetized retain the he mandrel and vacuum impregnated with a magnetization even when subjected to forces as suitable material, such as a phenolic condensawhich tend to demagnetize it, such as a properly ion pr duc ik B k li o m k he core limited alternating current field or ordinary rigid so that it will vibrate in a single mode with mechanical shock. no parasitic modes of vibration, and to further The invention can best be described as illusinsulate the core. The impregnated core I0 may trated by one particular form of magnetostrictive be embodied in the unit shown in Fig. 2 which device shown in the accompanying drawing in shows the impregnated spiral core l0 having a which: fabric tape covering Ii thereon, and a coil i2 Fig. 1 is a perspective view of one form in which wound over the covering H having leads I 5. The the vibrating element of the present invention combined structure of coil, core and covering is may be used; molded or cast in a plastic insulating body It.

M in which the core and all are cast the core against parasitic vito vibration of the are applied to the coil 12. Plastics and particularly phenolic condensation products are suitable for use as materials for the body. Such a method of enclosing the magnetostrictive element as described above is disclosed in the applications of E. E. Mott, Serial No. 549,970, filed August 8, 1944, now Patent No. 2,438,926, and Serial No. 617,001, filed September 18, 1945, now Patent No. 2,497,901.

' Other convenient methods oi insulating the magnetostrictive element may of course be used.

The body impregnated, it may be subjected to a magnetizing force from an applied current or an external permanent magnet sufliciently strong to magnetize it, preferably to at least its saturation point or near thereto, so as to cause it to be permanently magnetized in one direction.

The alloy treated according to the process of the present invention may be used in the magnetostrictive element in the form of a toroidal spirally wound tape core as described above, as well as in the form of stack-laminated cores made either irom circular rings or rectangular plates or in various suitable forms of other types.

The above-described magnetostrictive elements made from alloys of cobalt and iron, with or without vanadium, treated according to the process of the present invention may be used in general as electromechanical transducers in any device in which it is desired to convert electrical current variations into corresponding mechanical variations, or vice versa, or in which it is desired to use natural mechanical vibrational frequencies to control electrical frequencies, as in underwater sound projectors and microphones, frequencycontrol devices, electromechanical filters, telephone receivers and other devices. In general, the magnetostrictive devices of the present invention may be used in place of piezoelectric crystals device in which such crystals are used. Although specific embodiments of the invention have been shown and described, it will be understood that they are but illustrative and that various modifications may be made therein without departing from the scope and spirit of the invention.

What is claimed is:

l. A method of forming a vibratile magnetostrictive core comprising cold working, to a thickness reduction of at least 20 per cent, an alloy consisting of from per cent to 4 per cent vanadium, from 30 per cent to '70 per cent cobalt and the remainder essentially iron, forming said alloy into a laminated core and annealing said alloy in the cold worked state at a temperature of from 450 C. to 650 C.

2. A method of forming an annular radially vibratile magnetostrictive core comprising cold working, to a thickness reduction of at least 30 per cent, an alloy consisting of about 2 per cent vanadium, about 49 per cent cobalt and about 49 per cent iron to form it into a tape no greater than 6 mils in thickness, forming said tape into a spiral core, annealing said alloy in its cold worked state at a temperature of from 500 C. to 600 C. and magnetizing said core to near its saturation point.

S. The method of preparing an alloy having magnetic properties suitable for the formation of a vibratory magnetostrictive core adapted for operation without a biasing field, which method comprises cold working to a thickness reduction of at least 50%, an alloy containing, by weight,

about 2% vanadium and the remainder consisting of substantially equal proportions by weight of 5 iron and cobalt together with incidental impurities, and heat treating said cold worked alloy at a temperature between about 500 C. and about 600 C.

4. An annular, radially vibratile, electromechanical transducer comprising a permanently magnetized core of spirally wound tape formed of an alloy consisting essentially of about 49 per cent iron, about 49 per cent cobalt and about 2 per cent vanadium annealed at about 550 C. from a cold worked state produced by a cold thickness reduction of at least 20 per cent.

5. A device which functions through the magnetostrictive action'oi a magnetic metal element, said device comprising a magnetostrictive element formed of an alloy, consisting of between about per cent and about 4 per cent vanadium.

between about 30 per cent and about 70 per cent cobalt and the remainder essentially iron, annealed at a temperature between about 450 C. and about 650 C. irom a cold worked state pro duced by a cold thickness reduction of at least per cent.

6. An annular, vibratile, permanently magnetized, magnetostrictive core composed of a plurality of spirally wound turns of a tape having a thickness of about 2 mils, said tape being iormed of an alloy consisting of about 49 per cent cobalt, 2 er cent vanadium and the remainder essentially iron, said tape having been heat treated at a temperature of about 550 C. while in a cold worked state produced by a cold thickness reduction of at least 50 per cent.

'7. A magnetostrictive core composed of a plurality of laminations. each no greater than 6 mils in thickness and formed by cold working a body of a magnetostrictive alloy to a thickness reduction of at least 20 per cent and heat treating the body in the cold worked state at a temperature between about 500 C. and 600 C., said alloy consisting of between about per cent and about 4 per cent vanadium between about per cent and about 70 per cent cobalt and the remainder essentially iron.

8. A magnetostrictive core composed of a plurality of laminations of a magnetostrictive alloy formed by cold working a body of the magnetostrictive alloy to a thickness reduction of at least 20 per cent and heat treating the body in the cold worked state at between 450 C. and 650 C., said alloy consisting of between about per cent and about 4 per cent vanadium, between about 30 per cent and about 70 per cent cobalt and the remainder essentially iron.

9. An alloy having magnetostrictive properties and a substantial coercive force consisting of about 2 per cent vanadium, about 49 per cent cobalt and the remainder iron, said alloy having been treated by a process comprising cold working to a thickness reduction of at least 50 per cent and then heat treating in the cold worked state at a temperature of about 550 C.

10. An alloy having magnetostrictive properties and a substantial coercive force consisting of between about per cent and about 4 per cent vanadium, between about 30 per cent and about '70 per cent cobalt and the remainder essentially iron, said alloy having been treated by a process comprising cold working to a thickness reduction of at least 20 per cent and then heat treating v 7 8 in the cold wqrked state at between 450 C. and Number Name Date 650 C 1,857,215 Ruder L May 10, 1932 ETHAN A. NESBI'I'I. 1.862.559 White el; al June 14, 1932 HOWELL J. LLIAMS. 2,160,588 Granfield May 30, 1939 5 2,166,359 Lak-atos July 18, 1939 REFERENCES CITED 2,298,225 Nesbltt Oct. 6, 1942 The followin references are of record in 2,317,294 Nesbltt m- 1943 file 01 this patint: the 2,317,295 Nesbitt A l 20, 1943 UNITED STATES PA ENTS m FOREIGN PATENTS Number Name Date m r Country D e 1,441,522 Patterson Jan. 9, 1923 740,051 France Nov. 12, 1932 1,586,889 Elmen June 1, 1926 

